The last major innovation in hanging occurred toward the end of the 19th century, when executioners first developed a systematic way to calculate the drop. Once these “drop tables” were published, a hangman knew that he’d need 7 feet for a slight, 120-pound criminal, but only about 4 feet for a 200-pounder.

In the United States, only Washington and New Hampshire still perform hangings. These jurisdictions follow now-defunct U.S. Army regulations for the punishment. The military rules demand 30 feet of hemp rope that has been boiled, stretched, and dried. The bottom of the rope should be greased or waxed to make sure that the knot of the noose doesn’t get snagged, and the whole system should be tested with a sandbag dummy before the actual hanging takes place.

The Army even has its own drop table. According to its guidelines, the last man to hang in America—220-pound Billy Bailey—would have required 5 feet of loose rope. …

The Army drop table turned out to be inadequate for Mitchell Rupe, a Washington inmate who was supposed to hang in 1994. On death row, Rupe refused all exercise and ate junk food nonstop. By the time of his execution he’d reached 409 pounds, well above the table’s maximum listed weight. According to Army regulations, anyone heavier than 220 pounds would get a 5-foot drop. The Washington authorities made an exception and cut Rupe’s planned drop to 3.5 feet. Rupe appealed his case, and a federal judge ruled that the risk of decapitation was still too high. Rupe died in a prison hospital this past February.